Attachment for varying the magnifying power of telescopes



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Patented Sept. 8, 1925.

UNITED STATES PATENT OFFICE.

ARCHIBALD BARR AND WILLIAM STROUD, OF ANNIESLAND, GLASGOW, SCOTLAND, AS-

SIGNOBS T0 BARR AND STROUD', LIMITED, OF ANNIESLAND, GLASGOW, SCOTLAND.

ATTAGHMENT FOB. VARYING JMAGNIIF'YI1`l'Gr POWER OF TELESOO'PES.

Application led August 26, 1921.

Serial No. 495,551.

(GRANTED UNDER THE PROVISIONS 0F THE ACT 0F MARGH 3, 1921, 41 STAT. L.,1313.)

The object of our invention is to provide an attachment exterior to theeyepiece of a telescope or telescopic instrument (e. g., a rangender) tobe referred to in the claims generally as a primary telescope of such a.naine that thegsasalfying newer, may be' altered without 1n anywayraltering the focal plane of the primary telescope and withoutmaterially shifting the position of the exit pup-ill.

attachment according to this invention comprises a short Galileantelescope (i. e., a convergent lens of focal length F and a strongerdivergent lens of focal length 7' separated approximately by a distanceFf) or the attachment may comprise more than one short Galileantelescope, which or each of which may be inserted exterior to theprimary telescope between the eye and the ordinary eyepiece of thetelescopic instrument when required. One short Galilean telescope may beused to produce magnification only or diminution only, or it may be usedto produce either magnification or diminution by its being inserted inone or other of two attitudes (1) with the divergent lens nearer the eyein which case an increase of magnifying power will be produced (2) withthe convergent lens-nearer the eye in which case there will be produceda corresponding decrease in magnifying power. Thus with an attachmenthaving one short Galilean telescope, two or three magnifying powers willbe available. In the first case (1) without the Galilean telescope and(2) with the Galilean telescope in use. In the second case (1) withoutthe Galilean telescope (2) with the Galilean telescope in one attitude(3) with the-Galilean telescope reversed.

position betweenthe eye'. lens of thi any one may be brought into theproper po- A sition between the eye and the eyepiece.

In carrying out our invention it is desirable that the primary telescopeto which` the attachment is to be fitted should be provided with aneyepiece the constituent lenses of which are in close proximity so as toleave the maximum possible distance between the eyepiece and the exitpupil, in order to have room for the introduction of the attachment.

Several advantages are associated;4 with this method of producingvariable magnify-v lng power, e. g., l

Y (a) The attachment can be added to any existing telescope provided theeyepiece is suitable for the purpose.

(b) If the telescope has been made watertight or dust-tight the additionof the attachment does not introduce any source of leakage.

(c) If the telescope has a graticule, line l or other mark upon whichthe eyepiece 1s focussed the introduction of the attachment does notaffect this focus.

We are aware that attachments of the Y magnification may be the productof the' magnification of the two telescopes, but in all such cases withwhich we are acquainted the eye point (or exit pupil) has undergonematerial change in positlon. So far as we are aware, a short Galileantelescope has not previously been used as an attachment for producingvariable magncation by being inserted exterior to the telesoo at a vga.;

piece and the eye point (or exit pupil) of the primary telescope withoutnotable displacement of the sald eye point.

Some examples accordin to this invention will now be described witreference to the accompanying drawings, in which Figures 1 to 3 refer toa case where the eyepiece consists of two achromatic lenses inproximity. Figures 4, 5 and 6 refer to a case of an eyepiece of theRamsden type. Figure 7 represents a section and Figure S an end view ofa construction permitting of the introduction at will of either of twoGalilean (or kindred) systems one of which is shown in section in Figure7.

Figures 9, 10 and 11 refer to another method of introducing or removingthe Galilean system.

In all the Figures 1 to 6 and 9 to 11 the eye point is on the right-handside.

In Figures 1, 2 and 3, which represent three conditions of the sameeyepiece, the ordinary eyepiece is represented by the two achromaticlenses 1 and 2 in close proximityA (common practice in cases where it isdesired to have an eyepoint at some distance from the eyepiece). Therays of light represented correspond to those coming through theobjective (not shown) from a point of the object not on the axis 0f thetelescopic system. These rays after converging to the image point 3diverge and after traversing the eyepiece 1, 2 emerge as a parallel (ornearly parallel) beam in a condition to be in focus vwhen they fall upona normal eye placed at the eyepoint. Figure 2 represents the ordinarycase without the Galilean attachment. Figure 1 shows an attachment'inserted -in such a manner as to increase the magnification while Figure3 shows an attachment to roduce a diminution in the magnification. *achof these attachments which embodies the principal feature of the presentinvention is in all the cases shown represented' by the lenses 4 and 5of which 4 is a convergent lens of focal length, say, F, and 5 is adivergent lens of focal length f in which case the distance betweenv 4and 5 will be F--f. In the case of 4 (Figure 1) it will be desirable tomake 4 an achromatic combination, but in the case of 4 (Figures 3, 5 and6, where the magnification is less than il) it is frequently possible touse a simple ens.

In Figures 4, 5 and 6, Figure 4 corresponds to the case of an ordinaryRamsden eyepiece without any attachment, while Figure 5 and cases ineach of which the attachment produces a magnification which is less than1 in Figure 5 and mucli less than 1 in Figure 6. In the case of. aRamsden eyepiece it is generallyimpossible to use the attachment 4, 5 inthe manner of Figure 1 s0 as Figure 6 correspond to two' to roduce amagnification greater than 1` wit out producing a badly positioned eyeYpoint.

In the irst eyepiece represented in Figures l, 2 and 3, the medium poweris obtained by the eyepiece 1, 2 itself. The low wer is obtained byinserting the minifying Galilean combination 5, 4 and the high power byinserting a magnifying Galilean combination 4, 5.

In Figures 7 and 8, two Galilean attachments 6 and 7 are mounted and aclear aperture 8 is provided, as shown, upon a ring 9 which can beturned inside the ring 10 so that either 6, 7 or 8 may 'be brought intothe axis of the system.

In Figures 9 to 11 there is shown a further method of manipulating theGalilean system in and out or reversing it. In this case the system 4, 5is arranged so as to be rotatable at will about an axis perpendicular tothe paper midway between the two lenses. In Fi e 9 is lshown the highpower; after rotation of the system through' 90- the system is opticallyremoved as indicated in Figure 10, while after a further rotationthrough 90, as indicated in Figure 11, the lowest power is obtained.

We claim 1. An attachment to a primary telescope at the eyepiece endthereof and exterior to the telescope at a position between the eye lensof the eyepiece and the eyepoint comprising a short Galilean telescopeconsisting of a convergent lens and a stronger divergent lens separatedby a distance approximately equal to the difference in the focal lengthof the lenses, for the purposes set forth.

2. An attachment to a primary telescope at the eyepiece end thereof andexterior to the telescope at a position between the eye lens of theeyepiece and the eye point comprising a short Galilean telescopeconsisting of a convergent lens and a stronger divergent lens separatedby a distance approximately equal to the difference in the focal lengthof the lenses, the attitude of the Galilean telescope being such thatthe convergent lens is nearer the eye, for the purposes set forth.

3. An attachment to a primary telescope at the eyepiece end thereof andexterior to the telescope at a position between the eye lens of theeyepiece and the eye point comprising two short Galilean telescopes,each consisting of a convergent lens and a stronger divergent lensseparated by a distance approximately equal to the difference in thefocal length of the lenses, for the purposes setforth.

4. An attachment to a primary telescope at the eyepiece end thereof andexterior to the telescope at a positionv between the eye lens of theeyepiece and the eye point comprising 'a number of short Galileante1escopes, each consisting of a convergent lens and a strongerdivergent lens separated by a distance approximately equal to thedifference in the focal length of the lenses, and mounted capable ofbeing moved, for the purposes set forth.

5. An attachment to a primary telescope at the eyepiece end thereof andexterior to the telescope, a carrier mounted on the attachment capableof movement about a centre eccentric to the axis of the eyepiece of theYprimary telescope, a short Galilean telescope, consisting of aconvergent lens and a stronger divergent lens separated by a distanceapproximately equal to the difu', sul

ference in the focal length of the lenses,

mounted on the carrier, for the purposes set forth.

6. An attachment to a primary telescope at the eyepiece end thereof andexterior to the telescope, a carrier mounted on the attachment capableof movement about a centre eccentric to the axis of the eyepiece of theprimary telescope, a number of short`

